1. Field of the Invention
The present invention is broadly concerned with temporary wafer bonding compositions and methods of using the same.
2. Description of the Prior Art
Wafer thinning has been effectively used to improve heat dissipation in power devices and to fabricate flexible substrates, small chip packages, and multiple chips in a package. However, the reduction in wafer thickness combined with an increasing wafer diameter produces the tendency for the wafer to warp and fold, and thus creates a demand for new methods of wafer handling. Bonding substrate wafers to carrier wafers is one way of supporting brittle substrates such as GaAs, GaN, SiC, and InP during wafer thinning and backside processing. Of the different wafer-level bonding techniques, temporary wafer bonding using polymeric adhesives, followed by solvent or mechanical debonding, is becoming increasingly important for both integrated circuit and MEMS packaging, mainly due to its low cost, ease of processing, and adaptability to different substrate and device types. However, most of the currently available adhesives do not have adequate thermal or mechanical stability to withstand the high temperatures encountered in backside processing steps such as metallization, or dielectric deposition and annealing.
The major limitations of conventionally used adhesives such as waxes and commercial tapes for temporary wafer bonding include limited thermal stability at high processing temperatures, poor planarity (which contributes excessive total thickness variation across the wafer dimensions), and poor chemical resistance. To address these problems, a number of thermally stable bonding materials have been developed. Examples of these materials include polyimides, cyclic olefin copolymer compositions, cellulose derivatives, and rubber dispersed hydrocarbon resins. These materials require excessively high bonding pressures or bonding temperatures to achieve sufficient melt flow for good bond formation to occur. Consequently, this results in mechanical weakness when wafer processing at high temperatures, and causes process failures due to reflow of the bonding material in the bonded state. Alternatively, other materials such as thermosets have been used to overcome the reflow problem of thermoplastic adhesives. However, although thermosets are mechanically strong, they require complicated mechanisms for debonding, such as, laser rastering to release the carrier followed by peeling the adhesive from the surface of the thinned processed wafer. This can potentially cause serious damage to the thinned wafer. In addition, the residue often left on the device wafer is difficult to remove and can cause issues in downstream processing and device reliability.
Thus, there remains a need for new modes of carrier-assisted thin wafer handling that provide high wafer throughput and reduce or eliminate the chances for device wafer breakage and internal device damage.